One of the strongest earthquakes in state history startled Oklahomans Wednesday morning, rattling windows and nerves but causing no major damage or injuries.

Graduate student Joshua Dhanens was in th 6th floor break room of Dale Hall Tower on the University of Oklahoma campus when he and two associates felt the effects of a reported 4.3 magnitude earthquake with a center in east Norman, Oklahoma on Wednesday, October 13, 2010. "I've lived in California, so I wasn't too concerned." he said. He didn't, however, expect to be in an earthquake in Oklahoma. Photo by Steve Sisney, The Oklahoman. ORG XMIT: KOD

The quake was centered eight miles southeast of Norman, south of Lake Thunderbird, near E Post Oak Road and 84th Avenue SE, Oklahoma Geological Survey research seismologist Austin Holland said. He estimated the magnitude of the 9:06 a.m. quake at 5.1 and called it a "small to moderate earthquake," while the U.S. Geological Survey put it at 4.3.

Although there were only two reported minor injuries in Oklahoma, people were caught off guard by a jolting earthquake in the land of tornadoes.

Readers of The Oklahoman reported the quake felt or sounded like "a 747 landing in the neighbors' yard," "a semi hit our house" or "my house had been hit by a trash truck." People from seven states reported to the U.S. Geological Survey that they felt the quake, including from as far away as Brentwood, Tenn.

"That sucker it rattled my whole house, it literally shook the whole thing," said Charles Parnell, who lives in east Norman near Lake Thunderbird. "The chandelier jumped up and down a little bit, but there was no damage. It just surprised the heck out of me."

Paul Earle, a seismologist and director of operations for the U.S. Geological Survey's National Earthquake Center in Golden, Colo., said the discrepancy between the earthquake magnitude estimated by his agency (4.3) and that of the Oklahoma Geological Survey (5.1) results from different methods for monitoring earthquakes. Both types of measurement are valid, he said, even though they produce different results.

He said no major structural damage would be expected from quakes of this size in the United States.

Holland said his agency's 5.1 estimate likely will be reduced.

"I'm certain that we'll probably come down in our magnitude measurement because the USGS's 4.3 is so much lower than our 5.1. We keep track of the USGS magnitudes in our catalogs so we can improve. It's always good to compare your work to the foremost experts in the field of earthquake measurement."

Phone lines flooded

On Wednesday, Emergency Medical Services Authority in Oklahoma City said dispatchers received numerous calls relating to the earthquake. Most callers were having anxiety and worry over the earthquake, spokeswoman Lara O'Leary said, but two patients fell and needed medical care and were taken to Oklahoma City hospitals.